An electrical signal processing system may have a filter that removes a frequency band from the electrical signal. For example, the filter may supress noise within the frequency band. An example of such a filter is a microwave notch filter.
Ideally, the filter does not disturb the desired frequency components of the signal. Other desirable characteristics include a narrow attenuation response, high peak attenuation, and highly tuneable centre frequency. Designing a filter using prior art technology having all of the desirable characteristics may be difficult or impossible. One example of a prior art filter is a state-of-the-art microwave notch filter having an absorptive band-stop design, a 3 dB rejection bandwidth of 9.7 MHz, a 10 dB rejection bandwidth of 3 MHz, 30 dB peak attenuation, and a centre frequency of around 3.6 GHz. The centre frequency, however, may only by tuned over a 400 MHz range.